The present invention relates to a drain structure of a torque converter.
An automatic transmission having a drain oil passage for draining oil of a torque converter to a transmission case through an oil pump body has been proposed by the applicant of the present invention (see Japanese Patent Application Publication JP-A-2006-38065). The drain oil passage has an oil passage formed in the oil pump body so as to extend radially upward from a gap between an impeller hub of the torque converter and a boss portion of the oil pump body, and an oil passage formed on a fitting surface between the oil pump body and the transmission case. An intake preventing device for holding drain oil is provided on the side adjacent to an outlet port in the drain oil passage.
The intake preventing device prevents an intake of air from a discharge opening of the drain oil passage even when a small amount of oil leakage occurs from another oil passage that communicates with the torque converter. Thus, oil reduction of the torque converter is prevented in a state where oil supply is prevented. As a result, the occurrence of a phenomenon (lost drive) that causes the driver to feel uncomfortable due to a decrease in transmitted torque is prevented during a starting operation right after the engine is started after a vehicle has not been used for a long time.
The above intake preventing device is formed by an annular oil passage extending substantially entirely around the fitting surface between the oil pump body and the transmission case, a check valve, a fine mesh net, a trap oil reservoir, or the like. However, each of these elements discharges drain oil from an upper part of the oil pump body toward the inside of the transmission case. The drain oil is therefore directly scattered onto an upper part of an automatic speed change mechanism in the transmission case. Especially in the case where the impeller hub is supported by the boss portion of the oil pump body through a rolling bearing, a large amount of drain oil flows from the torque converter (e.g., 2 to 3 l/min). If the drain oil is scattered on a rapidly rotating drum or the like, the oil is stirred and bubbles are generated, thereby causing oil to blow from a breather hole. Moreover, in a disengaged state, the drain oil is scattered on a clutch or a brake disc and discs having differential rotation between separators, and a dragging torque is generated, thereby causing power loss.
On the other hand, the above Japanese Patent Application Publication JP-A-2006-38065 also discloses an embodiment in which the drain oil passage extends half around an oil passage formed on the fitting surface so as to reach the lowermost part of the oil pump body, and a pipe is connected thereto to drain the drain oil under the oil level in the oil pan (See FIGS. 3 and 4 and the second embodiment of Japanese Patent Application Publication JP-A-2006-38065).